Asynchrony in the timing of goose-vegetation interactions: implications for biogeochemical cycling in wet sedge tundra Tutakoke River, Yukon Delta NWR, Alaska, 2014-2016

Data were collected from a three-year manipulative experiment investigating the interacting effects of changes in plant phenology and timing of goose grazing on subarctic graminoid grazing lawns in the Yukon Delta NWR, Alaska, USA. Terrestrial high-latitude ecosystems are experiencing dramatic increases in temperature, changes in precipitation, and advancement of the growing season with important implications for trophic interactions. Uncoupling of the temporal relationships between migratory animals and the phenology of the forage they rely on for energy, nutrition, and rearing of young is one of the most glaring consequences of these changes. Furthermore, herbivores in high latitudes are likely to mediate biogeochemical responses to climate change substantially altering ecosystem function. However, little is known about how changes in the synchrony of herbivore-vegetation interactions will influence biogeochemical cycles. This research was conducted in the Yukon-Kuskokwim (Y-K) Delta in western Alaska, where there is strong evidence that climate change is driving temporal decoupling of the evolved linkage between the phenology of plants and the timing of goose migration. There is an urgency to the research because: 1) some of the most rapid climate changes in the world are underway in Alaska, leaving migratory geese and the ecosystem processes they influence vulnerable to new conditions, and 2) with the rapid advancement of the growing season, migratory goose feeding ecology is lagging substantially, threatening an irreplaceable subsistence resource for Native communities. The overall research objective is to quantify how an advancing growing season and changes in the synchrony of vegetation-goose interactions alter the magnitudes and patterns of C and N cycling in the YK Delta. Our specific research questions addressed with an experiment were: 1) How does the timing of plant growth interact with goose arrival time to alter summer-long magnitudes of plant production, foliar chemistry, and N availability? and 2) How does the timing of plant growth interact with goose arrival time to alter summer-long magnitudes of net ecosystem CO2 exchange, gross ecosystem photosynthesis, and ecosystem respiration?本数据集源自一项为期三年的操控性实验，该实验探究了植物物候（plant phenology）变化与鹅类放牧时机对美国阿拉斯加州育空三角洲国家野生动物保护区（Yukon Delta NWR）内亚北极禾本科草本放牧草地的交互影响。 陆地高纬度生态系统正经历气温显著上升、降水格局改变以及生长季提前的变化，此类变化对营养级交互作用（trophic interactions）具有重要影响。迁徙动物与其赖以获取能量、营养及抚育幼崽的饲草物候之间的时间关联解耦，是这些变化最突出的后果之一。此外，高纬度地区的草食动物可能会介导气候变化下的生物地球化学响应，进而大幅改变生态系统功能。然而，目前学界对草食动物-植被交互作用（herbivore-vegetation interactions）的同步性变化将如何影响生物地球化学循环（biogeochemical cycles）仍知之甚少。 本研究在美国阿拉斯加州西部的育空-库斯科奎姆（Y-K）三角洲开展，已有充分证据表明，气候变化正导致植物物候与鹅类迁徙时机之间演化形成的关联发生时间解耦。本研究具有迫切性，原因在于：其一，阿拉斯加正经历全球范围内最剧烈的气候变化之一，致使迁徙鹅类及其所调控的生态系统过程面临全新环境的胁迫；其二，随着生长季快速提前，迁徙鹅类的取食生态已大幅滞后，对原住民社区不可替代的生计资源构成威胁。 本研究的总体目标是量化生长季提前以及植被-鹅类交互作用同步性变化，将如何改变育空-库斯科奎姆三角洲碳（C）与氮（N）循环的强度与模式。本研究通过实验解答的具体科学问题包括：其一，植物生长时机与鹅类抵达时机如何交互作用，进而改变整个夏季的植物生物量、叶片化学组成及氮素有效性？其二，植物生长时机与鹅类抵达时机如何交互作用，进而改变整个夏季的生态系统净CO₂交换量、生态系统总光合速率及生态系统呼吸速率？